Gut Microbiota of 3 Beetle Larvae and Their Potential for Humic Acid Transformation

Abstract

With the rise in global temperature, the removal and long-term sequestration of CO2 from the atmosphere have become a shared global goal. Agricultural waste can be transformed by microorganisms into humic substances (HS) that are less prone to decomposition in soil, thereby increasing soil carbon sequestration. This study analyzed the gut microbiota of larvae from 3 different beetle species with varying diets. The gut microbiota of larvae from Trypoxylus dichotomus, which feed on decaying wood, were found to be richer and harbored a greater diversity of bacterial species compared to those of Alphitobius diaperinus and Araecerus fasciculatus. Further analysis of the gut microbiota isolated from 3 beetle larvae species examined the activity of enzymes involved in humic acid biosynthesis, including cellulase, ligninase, laccase, and tyrosinase. Among them, Bacillus megaterium BM01 and B. aryabhattai BA01 exhibited activities for all 4 enzymes, while B. subtilis BS01 showed activities for the first 3 enzymes. To further examine the ability of strains to convert rice straw into humic acid, B. megaterium BM01, B. aryabhattai BA01, and B. subtilis BS01 exhibited an increased humic acid conversion efficiency of 2.4%, 2.3%, and 2.1%, respectively, compared to the control group without inoculation. These findings suggest potential applications in on-site conversion and decomposition of residual rice straw post-harvest to humic acid, thereby enhancing soil carbon sequestration. 隨著全球氣溫攀升，移除大氣中的CO2 並長期封存已是全球的共同目標。農業廢棄物則可藉由微生物轉化為在土壤中不易分解的腐植質 (humic substances; HS)，以達到增加土壤碳匯的目標。本研究分析3 種不同食性的甲蟲幼蟲腸道微生物相，其中以取食腐朽木材的獨角仙 (Trypoxylus dichotomus) 幼蟲腸道菌相較外米擬步行蟲 (Alphitobius diaperinus) 及長角象鼻蟲 (Araecerus fasciculatus) 的幼蟲腸道菌相較豐富、菌種數量亦較多。進一步分析3 種甲蟲幼蟲腸道菌的腐植酸生合成相關酵素的活性，包括纖維素酶、木質素酶、漆酶及酪胺酸酶，其中Bacillus megaterium BM01 與B. aryabhattai BA01 可見上述4 種酵素活性，B. subtilis BS01 則有前3 種酵素活性。進一步檢驗菌株將稻草轉化為腐植酸的能力，其中B. megaterium BM01、B. aryabhattai BA01 及B. subtilis BS01，腐植酸轉換效率較未接菌種的對照組，各增加2.4%、2.3% 及2.1%。期待未來可應用於稻穀收穫後，田間殘存稻草的現地轉化分解成腐植酸，以達到增加土壤碳匯的目標。